Carburetor version. Not too many of them around now. "K" reg or there abouts?? Have a check of the 3 terminals in the distributor cap, clean them if they have any crud on them. Same goes for the Rotor Arm. Would have been a good idea to look at the condition of the spark plugs when you changed the leads. For what they cost it would be better to put 3 new ones in as it is one more thing eliminated.

If it still plays up after that then the next step is carburetor possibly the cold start side of things I would think or it could be electronics. You can get similar symptoms from either. Garage job on a gas analyser and electronics.